Key Takeaways

1. The correct command to flush DNS on modern macOS is sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder - both parts must run together.
   
2. Flushing DNS does not reset passwords, log you out of websites, or change your network settings.
   
3. You do not need to restart your Mac after flushing DNS, the change takes effect immediately.
   
4. Different macOS versions use different flush commands — always match the command to your OS version for it to work.
   
5. mDNSResponder is the macOS process that handles DNS resolution; restarting it with -HUP applies the flush without a full reboot.
   
6. Flushing DNS fixes errors like "This site can't be reached," outdated IP redirects, and post-migration website loading failures but will not increase raw internet speed.
   
7. Running the command requires administrator privileges; always enter your Mac login password when prompted.
   

What Does the Flush DNS Command Do on macOS?

The flush DNS command clears your Mac's locally stored DNS records and forces the DNS resolver service to start fresh. When you run sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder, your Mac discards all cached website-to-IP address mappings and rebuilds them by querying your DNS server on the next request.

Your Mac builds a DNS cache over time by saving the results of every domain lookup it performs. When you type "example.com" into a browser, macOS checks this local cache first before reaching out to an external DNS server. This process speeds up browsing considerably, but it becomes a problem when the cached data no longer matches reality. For example, after a website migrates to a new server or after a DNS record update is pushed by an administrator.

Flushing the cache removes all those stored records at once, forcing your Mac to fetch fresh, accurate data the next time you visit any website. The result is that stale, conflicting, or corrupted DNS entries are permanently cleared in seconds.

Breaking Down the Command

The command sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder is actually two separate instructions joined by a semicolon:

1. sudo — Runs the command with administrator-level permissions, which are required to modify system-level DNS data.
   
2. dscacheutil -flushcache — Clears the DNS cache stored in macOS's Directory Services cache utility.
   
3. ; — A shell operator that runs the second command immediately after the first finishes.
   
4. sudo killall -HUP mDNSResponder — Sends a "hang up" signal to the mDNSResponder process, causing it to reload its configuration without being fully terminated.
   

Running only one part of this command on modern macOS versions will produce an incomplete flush. Both parts are required for a full, effective DNS cache reset.

When Should You Flush DNS Cache on a Mac?

You should flush DNS cache on a Mac when you encounter browsing errors that point to stale or incorrect DNS data — such as sites that fail to load after a server migration, pages that redirect to the wrong destination, or connection errors on sites you know are online.

The most common situations that call for a DNS flush include:

1. Websites returning a "This site can't be reached" error even though you know the site is live.
   
2. A recently migrated website still loading the old version because your Mac cached the old server's IP address.
   
3. DNS-related SSL errors where the certificate doesn't match because the domain is resolving to the wrong IP.
   
4. Slow or inconsistent DNS resolution caused by a bloated or partially corrupted cache.
   
5. After changing your DNS server settings (e.g., switching to Google DNS or Cloudflare) and needing the change to take effect immediately.
   

You do not need to flush your DNS cache on a regular schedule. macOS automatically expires and refreshes DNS records based on each domain's TTL (Time to Live) value. Only flush when you have a specific browsing problem that points to a DNS conflict.

How to Flush DNS Cache on macOS?

Flushing DNS cache on macOS takes less than 60 seconds and requires only Terminal and your administrator password. Follow these steps exactly.

Step 1: Open Terminal

Launch the Terminal application on your Mac. You can do this in three ways:

1. Press Command + Space to open Spotlight, type Terminal, then press Enter.
2. Open Finder → Applications → Utilities → Terminal.
3. Use Launchpad, search for Terminal, and click it.

Terminal is a command-line interface that allows you to run system-level commands directly on macOS.

Step 2: Run the Flush DNS Command

Step 3: Enter Your Admin Password

After pressing Return, Terminal will prompt you with:

Step 4: Verify the DNS Cache Was Cleared

On modern macOS versions, a successful flush produces no output, a blank prompt is confirmation that it worked. However, you can verify the flush with a secondary check:

1. Open Safari or Chrome and visit a site that was previously broken.
   
2. Alternatively, open Terminal and run nslookup [domain] to see a fresh DNS lookup result.
   
3. On older macOS versions with verbose logging enabled, you may see a success message in the Console app.
   

If you receive an error message instead of a blank response, refer to the troubleshooting section below.

Flush DNS Commands for Different macOS Versions

Different versions of macOS use different DNS flushing commands. Using the wrong command for your OS version will either do nothing or return an error. Find your macOS version under Apple Menu → About This Mac and use the matching command.

If you are on macOS 10.15 Catalina or later, always use the full two-part command: sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder.

What is mDNSResponder in macOS?

When you run sudo killall -HUP mDNSResponder, you are sending a SIGHUP (Signal Hang Up) signal to the process. Unlike killing a process outright, SIGHUP instructs mDNSResponder to gracefully reload its configuration and discard its cached records — effectively applying the DNS flush that dscacheutil -flushcache initiated. This is why both commands must be run together: dscacheutil clears the cache data, and the mDNSResponder restart ensures the process picks up the cleared state.

Common Problems After Flushing DNS Cache

Most DNS flush attempts on macOS are straightforward, but a few errors can appear depending on your system configuration or macOS version.

Command Not Found

If Terminal returns command not found, you are likely using the wrong command for your macOS version. Check your macOS version under Apple Menu → About This Mac and use the correct command from the version table above. For example, macOS 10.10 Yosemite requires sudo discoveryutil udnsflushcaches, not the dscacheutil command.

Operation Not Permitted

This error appears when the command is run without sudo or when System Integrity Protection (SIP) is blocking the action. Always include sudo at the beginning of each part of the command. If SIP is causing the issue, you should not disable it — instead, confirm you are using the exact correct syntax and that your user account has administrator privileges enabled in System Settings → Users & Groups.

No Internet After Flush

A DNS flush does not cause internet disconnections — if your internet stops working after the flush, it was already failing before the command ran or the issue is unrelated to DNS. Check your Wi-Fi or Ethernet connection, confirm your DNS server settings in System Settings → Network, and try restarting your router. Running ping 8.8.8.8 in Terminal will tell you whether your connection itself is live.

Password Not Working

Terminal accepts your Mac login password, not your Apple ID or any other credential. If the password appears incorrect, confirm the right account has admin rights in System Settings → Users & Groups. Remember that no characters display while typing your password in Terminal — type carefully and press Return. After five failed attempts, you may need to wait or restart Terminal to try again.

Flush DNS Cache vs Restarting Your Mac

Flushing DNS cache and restarting your Mac both clear DNS records, but they are not equivalent operations. Flushing DNS is faster, targeted, and requires no downtime — it clears only the DNS cache and restarts only the DNS resolver process, leaving everything else untouched. A full Mac restart also clears DNS records but goes much further: it resets all running processes, clears RAM, restarts system services, and can resolve issues far beyond DNS.

If your only problem is a DNS-related browsing error, flushing the DNS cache is the correct and more efficient solution. It takes under 60 seconds compared to the 1–3 minutes a full restart requires, and it lets you stay in the middle of other work without closing open apps or losing unsaved data.

However, if you are experiencing broader system issues — slow performance, multiple services behaving unexpectedly, or network problems that persist after a DNS flush — a full restart may be the better next step. Think of a DNS flush as a scalpel and a restart as a reset button: use the right tool for the problem at hand.

How to Check DNS Records on macOS

You can check current DNS records directly from Terminal using the nslookup or dig command — both are built into macOS and require no additional installation.

1. Open Terminal.
   
2. Run: nslookup example.com — Replace example.com with any domain you want to check.
   
3. The output shows the DNS server used and the IP addresses the domain resolves to.
   

1. dig example.com — Returns the A record (IPv4 address).
   
2. dig example.com AAAA — Returns the IPv6 address.
   
3. dig example.com MX — Returns mail server records.
   
4. dig example.com NS — Returns nameserver records.
   

You can also check which DNS servers your Mac is currently using by running scutil --dns in Terminal. This outputs your full DNS configuration including search domains, resolver addresses, and query order — useful for confirming that a DNS server change has taken effect after flushing the cache.

Does Flushing DNS Improve Internet Speed?

Is It Safe to Flush DNS Cache on Mac?

Conclusion

FAQs

1. How often should I flush the DNS cache on Mac?
There is no recommended routine schedule for flushing DNS on a Mac. macOS automatically manages DNS record expiry based on each domain's TTL value. Only flush your DNS cache when you encounter a specific browsing problem that points to stale or incorrect DNS data, such as a site not loading after a known server migration or a persistent "This site can't be reached" error on a live site.

2. Will flushing DNS log me out of websites?
No. Flushing DNS cache has no effect on browser sessions, login cookies, or saved passwords. Your login state on websites is stored in your browser, not in the DNS cache. You will remain logged into every site you are currently signed into after running sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder.

3. Do I need to restart my Mac afterwards?
No restart is required. The DNS flush takes effect immediately after the command runs. The mDNSResponder process restarts itself within the command, so all subsequent DNS lookups automatically use the cleared cache. You can continue using your Mac and browsing the web right away.

4. Can flushing DNS fix "This site can't be reached"?
Yes, in many cases. The "This site can't be reached" error in Chrome and Safari is frequently caused by a stale or corrupted DNS record pointing to an old or invalid IP address. Flushing the DNS cache removes that bad record and forces a fresh lookup, which often resolves the error immediately. However, if the site itself is down or your internet connection is the problem, a DNS flush will not help.

5. What happens if mDNSResponder is restarted?
When you run sudo killall -HUP mDNSResponder, the process receives a SIGHUP signal and gracefully reloads its configuration, discarding all cached DNS records in the process. It does not shut down, it restarts within milliseconds. During that brief moment, any DNS query in progress is rescheduled automatically. There is no noticeable disruption to your network activity, and all Bonjour-based services (AirPlay, shared printers, etc.) continue working normally.